1. Field of the Invention
The present invention relates to novel ex situ processes for simple and economical destruction of air, water, and land contaminants.
2. Description of Related Art
Many industrial operations today utilize raw materials, solvents, and cleaners which result in the release of harmful pollutants into the environment. In addition, widespread use and improper disposal of toxic materials in the past have resulted in contamination of many soils and subsurface aquifers with harmful pollutants, particularly chlorinated aliphatic hydrocarbons (Council on Environmental Quality; U.S. Environmental Protection Agency, 1981). The National Priority List of the USEPA lists TCE as one of the most frequently reported contaminants at hazardous waste sites. In rural areas of the U.S., much of the drinking water supply is provided by groundwater. TCE is one of the most prevalent groundwater contaminants (Westrick et al. 1984; Lenhard et al. 1995), and due to the serious health threat these contaminated groundwaters pose, remedial action of such areas are of major concern. Traditional clean-up methods for contaminated water include air-stripping or air-stripping followed by granulated-activated carbon (GAC) adsorption. In either case, the contaminants are only transferred from one medium to another and must still be dealt with. In addition, traditional clean-up methods are often economically prohibitive due to the low concentrations of the contaminants. In contrast, biodegradation processes can convert toxic pollutants to non-toxic products such as carbon dioxide and water and are generally more economical than traditional clean up methods at low contaminant concentrations.
In industrial operations, tightening regulations are requiring more stringent controls on emissions and disposal, and chemical hygiene requirements are forcing the use of higher air volumes to provide worker safety, which results in high-volume, low-concentration contaminated air streams. Such contaminated air streams may be diluted to the point that traditional technologies, such as wet scrubbing, thermal oxidation, air stripping, or carbon adsorption may be either ineffective or too costly. Such dilute applications are well suited to biodegradation processes, which utilize microorganisms attached to natural or synthetic packing to actually biodegrade the target pollutants to non-toxic products rather than simply transfer them from one medium to another. Using biodegradation processes, contaminated streams are passed through packing containing microorganisms which degrade or mineralize the pollutants into harmless compounds such as carbon dioxide, salts, and water. In many cases, biodegradation processes provide cost-effective, environmentally friendly alternatives to traditional pollution control or remediation technologies.
The fate of chlorinated hydrocarbons, particularly TCE, is a major concern of the Department of Defense (DoD). Numerous DoD sites in the U.S. have been identified as having groundwater contaminated with chlorinated hydrocarbons as well as other hazardous organic compounds. The Army has prioritized xe2x80x9cSolvents in Groundwaterxe2x80x9d as the fifth highest requirement in the area of environmental cleanup research and development. At some DoD sites, contaminated groundwater is pumped to air strippers which remove the contaminants from the groundwater and transfer them to an air stream. In many cases, these contaminated air streams from the strippers are simply released to the environment. In addition, painting, coating, paint stripping, solvent degreasing, and other operations at DoD sites result in the release of streams contaminated with TCE, methylene chloride, and other harmful VOCs (volatile organic compounds) and SVOCs (semi-volatile organic compounds) to the environment. Economical and practical processes are needed to degrade such contaminants to harmless by-products, either directly in groundwater or wastewater, or in the air streams emitted to the environment from air stripping operations, from soil vapor extraction processes, or from other operations which release harmful pollutants.
Traditional contaminated groundwater clean-up methods include air-stripping and/or granulated-activated carbon (GAC) adsorption. Generally, the contaminated groundwater is pumped to the surface and then to the top of an air stripper, which usually consists of a cylindrical column packed with material designed to maximize liquid-to-air contact. The contaminated water flows down through the packing by gravity as air is blown up through the column. The volatile organic compounds are thus counter-currently stripped from the water and enter the air during transit through the stripper. In some cases, this contaminated air stream is then blown through an activated carbon filter designed for removal of the particular contaminants in question. However, the contaminants are not destroyed. They are simply held and concentrated within the carbon filter. At some point in time the carbon filter becomes saturated with contaminants, and then the contaminants begin to pass through the filter to the environment. At this time, it is necessary to replace the contaminated carbon with fresh carbon and to either dispose of the contaminated carbon or to send it to a vendor for regeneration, both of which are costly and inconvenient operations. In some cases, the groundwater may be pumped directly through carbon filters without first air stripping. In other cases, the groundwater is air stripped, the air from the air strippers is emitted to the environment, and the water effluents from the air strippers are passed through carbon filters to remove less volatile compounds which may not be removed by the strippers. Unlike carbon adsorption, biodegradation processes such as biofiltration can destroy the contaminants and offer practical, cost-effective, and environmentally friendly alternatives.
Biofiltration technology is being developed as an economical and environmentally friendly solution for a variety of remediation and pollution control applications. Example applications include both point and non-point source industrial emissions (regulated by the 1990 Amendments to the Clean Air Act) as well as site remediation waste streams generated by soil vapor extraction and air sparging systems. Biofiltration technology has been accepted in Europe for the last 50 years for the control of odors. Within the last decade, the technology is gradually being adopted in the U.S., and the application base is broadening to include the control of volatile organic compounds.
In most biodegradation processes, the microorganisms actually consume and derive food value from the target pollutants, and the waste stream can be passed continuously through the processes to achieve continuous degradation of the target pollutants in the waste stream. In other words, the microorganisms directly metabolize the pollutants as a source of food and growth. Such biodegradation processes will hereinafter be referred to as direct-metabolism processes. Pollutants capable of being directly consumed (or metabolized) by microorganisms in biodegradation processes include methyl ethyl ketone, methyl isobutyl ketone, butyl acetate, toluene, xylene, styrene, benzene, carbon disulfide, hydrogen sulfide, ammonia, and many others.
However, with certain pollutants, such as chlorinated aliphatic hydrocarbons and in particular the chloroethylenes, naturally occurring microorganisms cannot directly consume and derive food value from the pollutants. In other words, the microorganisms cannot directly metabolize the pollutants. In such cases, certain alternate carbon (food) sources, or primary substrates, can be supplied that the microorganisms directly metabolize, and in so doing, the microorganisms thereby generate enzymes capable of degrading certain target pollutants that cannot be directly metabolized. In other words, the pollutants targeted for destruction are indirectly degraded by enzymes generated when the microorganisms directly metabolize another compound in a process known as cometabolism. Hereinafter, such biodegradation processes shall be referred to as cometabolism processes. The alternate or primary food sources that the microorganisms directly metabolize can themselves also be pollutants or undesirable compounds such as toluene, or they can be relatively innocuous compounds such as glucose or propane.
Pollutants amenable to aerobic biodegradation via direct metabolism are those in which a wide variety of naturally occurring microorganisms can consume directly as sources of food, whereas pollutants requiring cometabolism for aerobic biodegradation are those in which the naturally occurring cannot consume directly as sources of food. Pollutants amenable to biodegradation via direct metabolism include a wide variety of organic compounds including alcohols, esters, ethers, ketones, aromatics, and alkanes, such as ethanol, butyl acetate, methyl tertiary butyl ether, methyl ethyl ketone, toluene, and propane, resectively, and other organic or non-organic compounds that may or may not contain halogens, sulfur, or nitrogen, such as methylene chloride, carbon disulfide, hydrogen sulfide, or ammonia. Pollutants requiring cometabolism for degradation include certain halogenated organic compounds, especially the chloroethylenes, such as tetrachloroethylene, trichloroethylene, dichloroethylenes, and vinyl chloride.
As will easily be appreciated by one skilled in the art, a direct metabolism process in accordance with the present invention is essentially a cometabolism process in accordance with the present invention except that the target contaminant cometabolic degradation step is omitted and only the direct metabolic metabolism step exists.
Obviously it is impossible to list all pollutants amenable to aerobic biodegradation via direct metabolism and those pollutants amenable to aerobic biodegradation via cometabolism. In fact, quite often there is no strict line of distinction between these two classes of pollutants, and some are amenable to aerobic biodegradation both direct metabolism and via cometabolism. Since direct metabolism is a simpler process, if a pollutant is amenable to aerobic biodegradation via simple direct metabolism, then direct metabolism will generally be the process of choice. On the other hand, if a pollutant is amenable to aerobic biodegradation via direct metabolism but the process is inefficient, then, generally speaking, aerobic biodegradation via cometabolism will be the process of choice.
Cometabolism processes are complicated by the fact that the target pollutants are not efficiently destroyed when the primary food sources are also present because the primary food sources compete with degradation of the target pollutants. In other words, when both the target pollutants and the primary food sources are present together, the microorganisms"" consumption (or direct metabolism) of the primary food sources greatly reduces degradation of the target pollutant through competitive inhibition. However, the degradation efficiency of the target pollutants can be improved by periodically withholding the primary food sources to allow the enzymes generated by direct metabolism of the primary food sources to degrade the target pollutants in the absence of the primary food source, thereby eliminating the deleterious effects of competitive inhibition.
TCE and other chlorinated aliphatic compounds can be cometabolically degraded by aerobic microorganisms if a primary carbon and energy source is available. Wilson and Wilson, 1985, first demonstrated aerobic degradation of TCE by soil samples amended with methane gas. Propane (Fliermans et al. 1988; Wackett et al. 1989), ammonia (Arciero et al. 1989), phenol (Hopkins et al. 1993), and toluene (Nelson et al. 1987) oxidizing microorganisms have also been reported to degrade TCE. Remediation systems containing methane-oxidizing bacteria, methanotrophs, have shown notable promise and have been extensively studied for the removal of TCE from contaminated streams. Methanotrophic isolate and mixed-culture systems have been studied in detail on the microcosm scale for determination of the optimum degradation environment and for degradation pathway determination (Brusseau et al. 1990; Fox et al. 1990; Little et al. 1988; Oldenhuis et al. 1989; Tsien et al. 1989). Furthermore, reactor experiments have been conducted (Fennell et al. 1993; Strandberg et al. 1989; Tschantz et al. 1995; Alvarez-Cohen and McCarty, 1991), and several studies have been reported where aquifer conditions were simulated in which methanotrophic organisms under proper stimulation degraded TCE (Semprini et al. 1990; Semprini et al. 1991; Wilson and Wilson, 1985). Methanotrophic systems continue to be investigated due to evidence that suggests that under the proper operating conditions, these methane-oxidizing microorganisms often degrade TCE at faster rates than other TCE degraders (Fennell et al. 1993; Chang and Alvarez-Cohen, 1995). Propane has been shown to stimulate TCE degradation (Phelps et al., 1991), and greater degradation efficiencies have been observed by manipulating or pulsing the primary substrate (Lackey, et. al. 1993). The teachings of the publications in this paragraph with regard to microorganism types and primary substrate types are hereby incorporated by reference and are discussed later in more detail, infra.
Several patents have been issued which teach microorganisms or methods for biodegradation of chlorinated compounds, some of which employ primary substrates (or primary food sources) to induce degradation of the target pollutants, including U.S. Pat. Nos. 4,452,894; 4,477,570; 4,664,805; 4,713,343; 4,749,491; 4,853,334; 4,859,594; 4,925,802; and 4,954,258; 5,079,166; and 5,543,317. The teachings of these patents with regard to microorganism types and primary substrate types are hereby incorporated by reference.
U.S. Pat. No. 4,452,894 teaches a microorganism composition capable of utilizing various halogenated aromatic compounds as sole sources of carbon without the need for primary substrate inducers, but it does not teach or claim said utilization of chlorinated aliphatic compounds, such as chloroethylenes, as sole carbon sources.
U.S. Pat. No. 4,477,570 teaches microorganism strains which degrade aromatic and halogenated aromatic compounds without primary substrates, but it makes no claim of degradation of chlorinated aliphatic hydrocarbons.
U.S. Pat. No. 4,664,805 teaches bacteria strains and in situ methods for accelerating the degradation of various halogenated organic pollutants, particularly polyhalogenated biphenyls, by addition of non-indigenous microorganisms and chemical analogs to contaminated environments. Careful balance of concentrations of the non-indigenous microorganisms, the indigenous microorganisms, and the chemical analog; competition between the indigenous and the non-indigenous microorganisms; and competition between the chemical analog and the halogenated metabolic by-products for degradation by the indigenous microorganisms diminish the practicality and economic viability of this method, as demonstrated by the low contaminant degradation rates obtained and long contact times required.
U.S. Pat. No. 4,713,343 teaches in situ methods for aerobically degrading halogenated aliphatic hydrocarbons in contaminated water by treating the water with microorganisms, alkane gases, and oxygen sources. The alkane gases are added to the contaminated water as carbon sources (primary food sources) to induce degradation of the target pollutants through an enzymatic pathway. The alkane gas inducers are thus co-mingled with the target contaminants of the environment, resulting in competition between the inducer and the target contaminants for degradation by the microorganisms. As prior art teaches, such co-mingling and competition between the inducer (primary food source) and target contaminants renders such methods cost prohibitive due to the low target contaminant degradation rates resulting from competitive inhibition of target contaminant degradation by degradation of the inducer. The low target contaminant degradation rates obtained using the methods taught in this patent are demonstrated by the long contact times required to achieve degradation of the target contaminants.
U.S. Pat. No. 4,749,491 teaches an in situ method for stimulating indigenous bacteria to degrade chlorinated hydrocarbons in water and soil through the addition of nutrients and oxygen sources such as hydrogen peroxide without the use of inducers such as propane or methane. Control of concentrations of the nutrients must be maintained such that overgrowth of microorganisms does not cause plugging of the substrata. In the teachings of this patent, no record or proof is demonstrated of the degradation of the subject contaminants by the subject indigenous microorganisms. Rather, claim is made to the relative degree of growth of unidentified microorganisms under aerobic laboratory conditions in the presence of said contaminants, said nutrients, and air or hydrogen peroxide. This said relative degree of growth is determined by subjective visual inspection of the relative degree of turbidity of the laboratory samples without identification of the microorganism species or any determination of its ability to degrade the subject contaminants.
U.S. Pat. No. 4,853,334 teaches a process using Pseudomonas fluorescens microorganisms to degrade haloaliphatic hydrocarbons, with or without carbon sources such as glucose or molasses as primary substrates to stimulate the bacteria to degrade the subject contaminants. However, the low degradation rates obtained and long contact times required are cost prohibitive and impractical for commercial applications. For example, only 2% of TCE present was degraded in 24 hours and only 13% of TCE present was degraded in 5 days.
U.S. Pat. No. 4,859,594 teaches microorganism strains and methods for genetically modifying, immobilizing, and utilizing said strains for degrading chloroethanes, chlorophenols, and PCPs without the use of primary substrates to induce degradation of the subject contaminants. However, the teachings make no provision or claim of degradation of chloroethylenes such as TCE. Furthermore, the genetically modified microorganisms are subject to competition by other microorganisms which may develop, thrive, and dominate when the subject biodegradation media are subjected to contaminants in the environment either incidentally or by choice other than those on which the said genetically modified organisms are adapted to dominate and thrive. Such competition and domination of alternate organisms which thrive on other contaminants can result in loss of capacity or function of genetically modified biodegradation media to degrade the contaminants they were adapted to degrade and intended to degrade.
U.S. Pat. No. 4,925,802 teaches a method for biodegradation of halogenated aliphatic hydrocarbons such as TCE by the addition of an aromatic amino acid primary substrate, in particular tryptophan, to induce degradation of the subject contaminants through activation of an oxygenase enzymatic pathway. An alternate method involves a preliminary step in which the microorganisms are first stimulated with the primary substrate to induce activation of the enzymes capable of degrading the subject contaminants followed by addition of the said stimulated microorganisms to the environment containing the subject contaminants, with or without additional inducer. However, with this method, presence of the inducer is required to sustain microbial production of the contaminant-degrading enzymes, and when the enzymes produced during the said preliminary stimulation step have been exhausted in the contaminated environment through degrading the subject contaminants, additional inducer or additional pre-stimulated microorganisms would be required to be added to the contaminated environment. Adding additional inducer to the contaminated environment introduces the competitive inhibition problems which exist with co-mingling of the inducer with the target contaminant. Adding additional pre-stimulated microorganisms to the environment would require a dedicated process for production of pre-stimulated microorganisms for repeated additions to the contaminated environment until such time that satisfactory decontamination was accomplished, thus substantially increasing remediation costs. In addition, the said dedicated process for production of pre-stimulated microorganisms would be required to be capable of completely consuming the said inducer prior to introduction of the said pre-stimulated microorganisms to the contaminated environment or the residual inducer would be introduced as well into the environment, thus co-mingling the inducer with the subject contaminants and thus reducing the efficiency and economic viability of the process.
U.S. Pat. No. 4,954,258 teaches improvements in prior art methods for alkane-induced, methanotrophic bacterial degradation of halogenated aliphatic hydrocarbons in water (as in U.S. Pat. No. 4,713,343, Wilson et al.) by substituting part or all of the alkane inducers with lower alkanols, in particular methanol. The subject patent teaches that the substituted alkanols provide an alternate carbon source for growth of the methanotrophic bacteria and that the alkanols do not substantially bind with methane monooxygenase, the enzyme required for degradation of the halogenated aliphatic hydrocarbons, and thus the alkanols do not competitively inhibit degradation of the subject contaminants in the way that alkanes do by competing for the methane monooxygenase. Rather, the alkanols are metabolized by methanol dehydrogenase. However, methane monooxygenase is required for degradation of the halogenated aliphatic microorganisms. Therefore, when the methane monooxygenase supply is exhausted through degradation of the halogenated aliphatic hydrocarbons, methane or other stimulus must be added to the system to stimulate production of additional methane monooxygenase if degradation of halogenated hydrocarbons is to continue. The substituted methanol provides a carbon source for growth of the methanotrophic bacteria but does not activate the methane monooxygenase enzyme required for the intended degradation of the halogenated aliphatic hydrocarbons. Thus, to continue degradation of the subject contaminants, adding additional methane or other methane monooxygenase inducing stimuli to the contaminated environment or biodegradation media is required until such time that the environment or contaminated media is satisfactorily decontaminated, which allows co-mingling of the methane monooxygenase inducer with the subject contaminants and the associated competitive inhibition problems which substantially reduce efficiency and economic viability. The low degradation rates demonstrated with use of the above taught method are cost prohibitive and preclude its economical use in commercial applications.
U.S. Pat. No. 5,079,166 teaches a method for degradation of TCE by treating TCE with genetically engineered and isolated microorganisms containing a recombinant plasmid which contains toluene monooxygenase genes. The microorganisms of the subject patent must have been treated with an inducer of the toluene monooxygenase genes. This method avoids the complications of competitive inhibition associated with co-mingling of the inducer with the contaminant, but the genetically engineered microorganisms are not capable of sustaining degradation of TCE on their own in the contaminated environment or degradation media. New genetically engineered microorganisms must be continually grown in a separate controlled environment and continually added to the contaminated environment until such time that decontamination is complete, or they must be continually added to a continuous ex situ bioreactor process to sustain the degradation capacity of such bioreactor until such time that operation of the bioreactor is no longer needed or desired. Furthermore, the low degradation rates and long contact times demonstrated by the methods of this invention as well as the requirement for repeated separate-environment growth and addition of the genetically engineered microorganisms render the method cost prohibitive for commercial operations, particularly for the case of ex situ bioreactor processes, requiring a period of hours for substantial degradation TCE.
U.S. Pat. No. 5,543,317 teaches a bacterium capable of degrading hazardous chemicals, including chloroethylenes and TCE, without the use of a primary substrate to induce degradation of the subject contaminants. However, the said microorganisms are genetically engineered microorganisms, and therein exists several aforementioned disadvantages with use of such organisms in natural environments. Such disadvantages can include additional processing costs, process complications, and process inefficiencies for the genetically engineered methods as described above concerning U.S. Pat. No. 5,079,166. Genetically engineered pure microorganism cultures generally are not capable of sustaining their populations and thus their degradation efficiencies in the diverse contaminated environments encountered in nature and therefore must be continually or periodically replenished due to competing bacteria as well as competing substrates and contaminants. The low degradation rates (1.3 mg TCE/L/day) and long contact times (overnight incubation) demonstrated in this patent (U.S. Pat. No. 5,543,317, supra) as well as the need for repeated separate controlled environment growth and addition of the genetically engineered microorganisms render the method cost prohibitive for commercial operations, particularly for the case of ex situ bioreactor processes, requiring an overnight period for substantial degradation of TCE.
Prior art teaches that ex situ biofilters and bioreactors are akin to microorganism zoos, with the microorganism cultures naturally adapting, dominating, and maintaining themselves according the various compounds, food sources, and contaminants present or fed to the biodegradation media. Biofilters and bioreactors can be inoculated with pure microorganism cultures, genetically engineered microorganism cultures, mixtures of various cultures, groundwater, soil sediments, or sewage sludge, but the inoculated cultures generally do not sustain themselves in their original inoculated type and makeup in the biodegradation media with the myriad of other indigenous microbes, substrates, and contaminants being fed to a biofilter or bioreactor from sources open to the atmosphere and elements. There occurs adaptations and changes within the microbial populations in the biodegradation media to those cultures which best survive and thrive on what is available in the natural environment or waste stream to be remediated or otherwise purified of contaminants. Such natural environments generally include a myriad of indigenous microorganisms, contaminants, food sources, and compounds other than those present in external controlled environments manipulated to cause domination and purification of specific cultures for degrading the compounds in the natural environment targeted for detoxification. When such pure cultures are subjected to such natural environments, either in situ or ex situ, changes in the microbial populations generally occur to favor those organisms which best thrive in the natural environments or in the bioreactor which is receiving the contaminated stream from a natural environment or other operation exposed to the natural environment.
Indeed, there is no need for initial inoculation of biofilters or at all, since a myriad of naturally occurring microorganisms is present everywhere in the environment, and the waste streams containing the target contaminants fed to the ex situ biofilters or bioreactors from the natural environment already contain diverse wild type microorganisms that have adapted to sustain themselves in the presence of the target contaminants, similarly to the way in which wild yeasts in the environment degrade sugars present in fruit into alcohol. The biofilters or bioreactors function to immobilize, feed, and concentrate the microorganism cultures which best degrade the target contaminants. Thus, when biofilter or bioreactor operations are initiated without an initial inoculum, the diverse wild type microorganisms present in the surrounding environment and in the waste streams containing the target contaminants enter the biofilters or bioreactors and adapt, change, grow, and dominate to those cultures which best survive and thrive on the contaminated streams, food sources, and nutrients present or passing through the biofilters or bioreactors. Pre-isolation and concentration of microorganism cultures for initially inoculating biofilters or bioreactors may reduce start up time but is not necessary, since changes, adaptations, and dominance of certain cultures will occur even in such isolated and inoculated cultures after operation begins and the biofilters or bioreactors are subjected to complex mixtures of food sources, contaminants, and microorganisms present in the natural environment.
There appears no prior art in which the Applicants are aware of the ex situ cometabolic or direct metabolic processes of our invention utilizing our novel closed-loop recycle schemes that (1) provide efficient and complete direct metabolism of primary substrates (food sources), whether they themselves be pollutants or harmless compounds, without loss or venting of the primary substrates to the environment, (2) allow enzymatic degradation (cometabolism) of sorbed or residual target contaminants during feeding of the primary substrates to the microorganisms without loss or venting of the primary substrates or target contaminants to the environment, (3) virtually preclude co-mingling of primary substrates with target contaminants and thereby achieve high target contaminant degradation efficiency, (4) utilize naturally occurring microorganisms widely available in the environment, and (5) self-optimize to maintain the optimal microbial types and populations without the need for microorganism replenishment or modification.
The present invention relates to novel, efficient, and economical ex situ processes utilizing closed-loop recycle schemes for cometabolic degradation of chloroethylenes or other amenable target contaminants which alone are not easily or efficiently degraded by naturally occurring microorganisms and for direct metabolic degradation of a wide variety of other amenable contaminants. The processes of the present invention are not limited to utilization of any particular type of microorganism and preferably utilize naturally occurring microorganisms which are widely available in the surrounding environment and that are easily obtainable from sources such as soil sediments, groundwater, or in the contaminated streams to be treated and that are widely taught in the prior art, supra. Examples of such naturally occurring microorganisms which may be utilized in the processes of the present invention include those discussed in the prior art previously incorporated by reference.
The processes of the present invention for cometabolic degradation utilize primary substrates (alternate food sources) to induce enzymatic degradation (cometabolism) of target pollutants which alone are not easily or efficiently biodegraded by such naturally occurring microorganisms, such as is the case with chloroethylenes, particularly TCE. Further, the processes of the present invention for cometabolic degradation are operated in a cyclical fashion such that feeding of the targeted waste or contaminated streams is separated from feeding of the primary substrate streams into separate and discrete process cycles to minimize or eliminate co-mingling of the primary substrate with the target contaminants. Most importantly, the processes of the present invention utilize novel closed-loop recycle schemes which dramatically improve the efficiency, economics, and practicability of such. During closed-loop recycle periods, the processes are virtually closed to the outside environment with little or no net process flows entering or leaving the processes. These novel closed-loop recycle schemes can be employed for direct metabolism of food sources, whether they be pollutants, undesirable compounds, or innocuous compounds, and/or for cometabolism of target contaminants incapable of direct metabolism. For contaminants requiring degradation by cometabolism, the novel closed-loop recycle schemes can be employed not only during the microorganism feeding periods (direct metabolism), but during the target contaminant degradation periods (cometabolism) as well. In addition, these novel closed-loop recycle schemes can be employed for high-efficiency destruction of a wide variety of pollutants and undesirable compounds that are capable of microbial degradation by direct metabolism in a simplified process without a cometabolic degradation cycle. In such simplified direct metabolism processes, the food sources for the microorganisms are the pollutants targeted for destruction and the processes are closed to outside environment except for short periods to replenish microorganisms in the closed system with fresh air. The novel closed loop recycle schemes of the present invention may be used for treating either gas- or liquid-phase streams containing contaminants capable of direct metabolism and/or contaminants requiring cometabolism. The processes may be applied on a batch or continuous basis to contaminated soil and groundwater, to contaminated effluents from a wide variety industrial operations such as solvent degreasing, or to wherever amenable contaminants are present.
Chloroethylenes, particularly TCE, are known to be difficult to biodegrade aerobically to non-toxic products without the employment of a primary substrate to feed the microorganisms and thereby induce cometabolic degradation of the chloroethylenes through an enzymatic pathway. Ordinarily, practical and economical enzymatic degradation of chloroethylenes via a primary substrate is not possible because direct metabolism (consumption) of the primary substrate itself competes with enzymatic cometabolic degradation of the target pollutants, thus rendering degradation of the target pollutant inefficient and economically prohibitive. In the processes of the present invention for cometabolic degradation, pulsing the primary substrate stream with the contaminated stream, or in other words, alternating flow of the primary substrate with flow of the contaminated stream to be detoxified in a cyclic fashion, improves economic viability over processes which allow simultaneous presence of both the primary substrate and the target contaminants in the packing or other biodegradation media. However, in practice, a substantial quantity of chloroethylenes or other amenable contaminants sorb to the biodegradation media during flow of the contaminated stream, and when the primary substrate stream is again returned to the process to sustain the microorganisms and generate enzymes needed for target contaminant degradation, presence of the primary substrate causes the residual and sorbed target contaminants to desorb from the biodegradation media and escape to the environment, resulting in a substantial loss of process efficiency and economics. Furthermore, practical contact times required for economical commercial operation dictate the incomplete utilization (direct metabolism) of the primary substrate during single-pass and/or open-loop process flow, and its co-mingling with the target contaminants when they are again returned to the system results in competitive inhibition of target contaminant degradation, allowing the target contaminants to pass through the process undegraded and further decreasing process efficiency and increasing process cost.
We have unexpectedly found that, for cometabolic processes, practicing the processes of the present invention utilizing novel closed-loop recycle operation schemes take advantage of the adsorption-desorption dynamics within the biodegradation media and unexpectedly (1) provide efficient and complete direct metabolism of primary substrates (food sources), whether they themselves be pollutants or harmless compounds, without loss or venting of the primary substrates to the environment, (2) allow enzymatic degradation (cometabolism) of sorbed or residual target contaminants during feeding of the primary substrates to the microorganisms without loss or venting of the primary substrates or target contaminants to the environment, (3) virtually preclude co-mingling of primary substrates with target contaminants and thereby achieve high target contaminant degradation efficiency, (4) utilize naturally occurring microorganisms widely available in the environment, and (5) self-optimize to maintain the optimal microbial types and populations without the need for microorganism replenishment or modification, thus dramatically improving the simplicity, economics, and practicability of such processes.
Scientific wisdom indicates that said closed-loop recycle schemes should deplete the oxygen supply in the closed system, resulting in loss of the aerobic microorganisms and failure of the process. However, the novel closed-loop recycle schemes of the present invention unexpectedly result in dramatic improvements in process efficiency and economics while self-optimizing the microbial types and populations to the chosen primary substrate(s) (in cometabolic processes) and the site-specific target pollutants and other environmental characteristics.
With use of the novel closed-loop recycle schemes of the present invention for cometabolic or direct metabolic processes, oxygen demand for the primary substrate and/or pollutant should deplete the oxygen supply, kill the aerobic microorganisms, and render the process useless. Unexpectedly, oxygen levels are reduced only slightly, defying conventional scientific wisdom concerning the function of the aerobic microorganisms. The closed loop recycle schemes dramatically reduce use (cost) of the primary substrate, eliminate target pollutant emissions during feeding of the microorganisms, and reduce overall pollutant emissions, which in turn dramatically improves process efficiency and reduces process capital and operating costs.
We have also unexpectedly found that, for pollutants capable of biodegradation via direct metabolism only, practicing the processes of the present invention utilizing novel closed-loop recycle operation schemes take advantage of the adsorption-desorption dynamics within the process and unexpectedly (1) provide efficient and complete direct metabolism of the contaminants without loss or venting of the contaminants to the environment, (2) utilize naturally occurring microorganisms widely available in the environment, and (3) self-optimize to maintain the optimal microbial types and populations without the need for microorganism replenishment or modification, thus dramatically improving the simplicity, economics, and practicability of such processes.
It is therefore the principal object of the present invention to provide novel, efficient, and economical ex situ processes utilizing closed-loop recycle schemes for cometabolic enzymatic degradation of chloroethylenes and other amenable contaminants which alone are not easily or efficiently degraded by naturally occurring microorganisms and for direct metabolic degradation of a wide variety of other amenable contaminants.
Another object of the present invention is to provide said cometabolic processes such that flow of the waste or contaminated streams is substantially separated from flow of the primary substrate streams into separate and discrete process cycles to minimize or eliminate co-mingling of the primary substrate with the target contaminants to avoid loss of contaminant degradation efficiency.
A further object of the present invention is to provide said processes with microbially self-optimizing characteristics which force the adaptation, dominance, and maintenance of the microbial types and populations that provide optimal degradation of the target contaminants, without the need for addition or replenishment with pure, externally grown strains of microorganisms, and rather, allowing no initial inoculation or the initial inoculation of the processes with the waste stream to be detoxified or with soil sediments or water collected from widespread environments which are contaminated with the target contaminants or other site-specific amenable contaminants targeted for detoxification.
A still further object of the present invention is to provide said cometabolic processes with novel closed-loop recycle schemes in which the processes are periodically closed the outside environment and the enclosed process streams are recirculated within the process which (1) provide efficient and complete direct metabolism of primary substrates (food sources), whether they themselves be pollutants or harmless compounds, without loss or venting of the primary substrates to the environment, (2) allow enzymatic degradation (cometabolism) of sorbed or residual target contaminants during feeding of the primary substrates to the microorganisms without loss or venting of the primary substrates or target contaminants to the environment, (3) virtually preclude co-mingling of primary substrates with target contaminants and thereby achieve high target contaminant degradation efficiency, (4) utilize naturally occurring microorganisms widely available in the environment, and (5) self-optimize to maintain the optimal microbial types and populations without the need for microorganism replenishment or modification, thus dramatically improving the simplicity, economics, and practicability of such processes.
A still further object of the present invention is to provide said direct metabolic processes with novel closed-loop recycle schemes in which the processes are periodically closed the outside environment and the enclosed process streams are recirculated within the process which (1) provide efficient and complete direct metabolism of the contaminants without loss or venting of the contaminants to the environment, (2) utilize naturally occurring microorganisms widely available in the environment, and (3) self-optimize to maintain the optimal microbial types and populations without the need for microorganism replenishment or modification, thus dramatically improving the simplicity, economics, and practicability of such processes.
Still further and more general objects and advantages of the present invention will appear from the more detailed description set forth below, it being understood, however, that this more detailed description is given by way of illustration and explanation only and not necessarily by way of limitation, since various changes therein may be made by those skilled in the art without departing from the true scope and spirit of the instant invention.